1. Field of the Invention
The present invention is directed to an epoxy resin encapsulating material for molding in a semi-conductor chip and method of preparing the same.
2. Description of the Prior Art
Encapsulation of semiconductor chips has been made by a transfer molding using so-called tablets of an encapsulating composition composed of an epoxy resin, a curing agent, and an inorganic filler. The tablets are prepared by the steps of kneading the encapsulating composition and processing the same into a semi-cured body in the form of a sheet or wire, pulverizing the solid body into granules followed by being compacted into a cylindrical form. Thus prepared tablets are fed in a pot of a transfer-molding device and are forced into a mold cavity where they are molded to surround the semiconductor chip. Nowadays, there is proposed for enhancing encapsulation quality to use a multi-pot transfer molding device in which a plurality of pots are provided to encapsulate a plurality of the semiconductor chips at once with reduced length of runner leading from the pot to the associated mold cavity. As the number of the pots increases, the size of the tablets are required to be reduced to give the sufficient number of the tablets into each pot. In this respect, it is envisaged to utilize the pulverized granules of the encapsulating composition prior to being compacted into the tablet.
However, the granules after being pulverized from the semi-cured epoxy composition inherently includes a number of minute particles which are very likely to clog passages for supplying the encapsulating material to a metering section of the transfer molding device and for supplying it to the pots, thereby failing to supply a sufficient amount of the material to the mold cavity with attendant poor encapsulation. Such minute particles have a tendency to adhere to the large granules, they are difficult to be filtered out by the use of a sieve and are easily separated from the large granules when subjected to vibrations applied in the course of feeding the granules to the pot and/or the molding cavity. Further, the granules may be chipped at their corners when subjected to the vibrations to add resulting minute particles.
Even by the use of the tablets, the minute particles are easily separated from the tablets when subjected to the vibration while being fed to the pots and/or the cavities, thereby causing undesired clogging of the passages to the cavities.
In view of the problems, it is demanded to provide the epoxy encapsulating material in the form of the granules which can successfully avoid to clog the passages of the material in the transfer molding device.